1. Field of the Invention
The present invention relates to a developing apparatus employed for an image forming apparatus employing an electro-photography method or electrostatic recording method, for example.
2. Description of the Related Art
As for a developing method employing monocomponent toner serving as an existing developer, a contact developing method and a non-contact developing method have been widely employed. Specifically, (1) Contact developing method employing a developing roller serving as a developer bearing member having an elastic layer, (2) Non-contact developing method with nonmagnetic toner employing a developing roller serving as a developer bearing member including a metal sleeve or elastic layer, (3) Non-contact method with magnetic toner employing a metal sleeve serving as a developing bearing member, and so forth, have been proposed. As for a developer amount regulation member configured to regulate the amount of developer to subject monocomponent toner to thin-layer formation on a developer bearing member as to those developing methods, several measures have been proposed.
(1) Contact Developing Method Employing Developing Roller Having Elastic Layer (FIG. 10)
A method has been widely known wherein developing is performed by bearing nonmagnetic developer on a developing roller 3 serving as an elastic roller having a dielectric layer, and making this contact with a photosensitive drum 1. Supply of a developer to the developing roller 3 is performed by a supply roller 5 which is in contact with the developing roller 3. The supply roller 5 includes a function of transporting a developer from within a developer container T, making the developer adhere to the developing roller 3, and temporarily eliminating the developer remaining on the developing roller 3.
The application of charge due to the layer regulation and frictional charge of a developer adhered to the developing roller 3 is performed by causing a developer amount regulation member 4-c to make contact with the developing roller 3. As for the developer amount regulation member 4-c, it has been proposed to employ a blade-shaped metal thin plate, which is supported along one side in the longitudinal direction, with the underside of the facing portion thereof in contact with the developing roller 3. The developer coated on the developing roller 3 develops the electrostatic latent image formed on the photosensitive drum 1, and bias potential applied on the developing roller 3. As for the method of (1), Japanese Patent Laid-Open No. 2001-92201 has been known.
(2) Non-Contact Developing Method with Nonmagnetic Toner Employing Developing Roller Including Metal Sleeve or Elastic Layer (FIG. 11)
A method has been widely known wherein a developer is carried and held on a developing sleeve 3a having a cylindrical metal or a conductive resin layer on the surface thereof, and developing is performed by non-contact with the adjacent photosensitive drum 1 surface. Supply of a nonmagnetic developer to the developing sleeve 3a is performed by the supply roller 5, as with (1) Contact developing method.
The application of charge due to the layer regulation and frictional charge of a developer adhered to on the developing roller 3 is performed by causing a developer amount regulation member 4-c to make contact with the developing sleeve 3a. In the event of employing a developing roller including an elastic layer, it has been proposed to employ a blade-shaped metal thin plate which is supported along one side in the longitudinal direction, and the underside of the facing portion thereof is in contact with the developing roller, as with (1) Contact developing method. Also, in the event of employing the developing sleeve 3a having high rigidity, it is difficult to employ a metal plate serving as the developer amount regulation member 4-c to contact with the developing sleeve 3a. So it has been proposed to employ a metal thin plate on which a resin layer including some elastic properties is coated, and the like.
Not only DC bias but also AC bias is applied between the developing sleeve 3a and the photosensitive drum 1. The developer coated on the developing sleeve 3a with the developer amount regulation member 4-c flies and goes back and forth between the photosensitive drum 1 and the non-contact developing sleeve 3a by this AC bias. Also, an electrostatic latent image formed on the photosensitive drum 1 is developed by the potential of the DC bias applied to the developing sleeve 3a. 
(3) Non-Contact Method with Magnetic Toner Employing Metal Sleeve (FIG. 12)
A non-contact developing method employing monocomponent magnetic toner has been widely known. This method is the same as (2) Non-contact developing method employing nonmagnetic toner in that the cylindrical developing sleeve 3a is employed, and in that the application of charge due to the layer regulation and frictional charge of a developer is performed by causing the developer amount regulation member 4-c to make contact with the developing sleeve 3a. However, with the non-contact developing method, supply of a developer to the developing sleeve 3a is performed with magnetic force by providing a magnet 7 within the developing sleeve 3a. As for the method of (3), Japanese Patent Laid-Open No. 54-43027, and Japanese Patent Laid-Open No. 55-18656 have been known.
DC bias and AC bias are applied between the developing sleeve 3a and the photosensitive drum 1 as with (2) Non-contact developing method employing nonmagnetic toner, and development is performed by non-contact. At this time, even if there is too much toner having insufficient electrification properties on the developing sleeve 3a, the toner is prevented from being developed unnecessarily by disposing a magnetic pole near the developing portion. Accordingly, with regard to the electrification properties of the developer on the developing sleeve 3a, strict control as much as (2) Non-contact developing method employing nonmagnetic toner is not requested. As for the developer amount regulation member 4-c, it has been proposed to employ a rubber plate having low contact pressure as compared with (2) Non-contact developing method employing nonmagnetic toner by taking stability of contact as to the developing sleeve 3a into consideration.
Heretofore, as for a developer amount regulation member, a blade-shaped developer amount regulation member has been known, which supports a thin-plate elastic member along one side in the longitudinal direction, and causes the underside of the facing portion thereof to make contact with the developing roller.
Also, a developer amount regulation member has been known in Japanese Patent Laid-Open No. 6-250509, which fixes both ends of a plate-shaped elastic body to a holding member, and causes the center portion of the plate-shaped elastic body to make contact with a developing roller.
An existing developer amount regulation member, which supports a thin-plate elastic member and causes the underside of the facing portion to make contact with a developing roller, has a problem in that reduction in size is difficult. Upon reduction in size being performed on such a developer amount regulation member, the distance from a supporting point where the thin plate is supported along one side in the longitudinal direction to a contact point with the developing roller, i.e., free length is shortened. Thus, the spring constant of the contact pressure increases, and if the setting position of the developer amount regulation member is changed even slightly, the contact pressure greatly changes. Accordingly, in order to set stable contact pressure, assembly with high precision is necessary.
Also, shortening the free length of the thin-plate elastic member enables the influence of the adhesion unevenness and so forth at a supporting portion along one side in the longitudinal direction to be readily received. As such, it is difficult to apply uniform contact pressure over a longitudinal direction, which further makes it difficult to realize reduction in size.
Also, in the event of employing a developer amount regulation member according to known technology, it is difficult to set a desired local maximum value of contact pressure in a stable manner, and the variation in local maximum values of contact pressure is readily caused in the longitudinal direction of the developer amount regulation member. Accordingly, the variation in toner degradation conditions occurs over the longitudinal direction after endurance (long-term use of developing apparatus), and consequently, leading to a problem wherein concentration unevenness occurs over the longitudinal direction in a solid image after endurance.
In the event of forming toner in a thin layer by employing a developer amount regulation member according to known techniques, a developing roller serving as a developer bearing member is pressed against the underside of a blade (surface except for the edges of the blade) serving as a developer amount regulation member. Accordingly, regarding pressure distribution of contact nip portion between the blade and developing roller, contact pressure becomes the maximum at the nip portion center, and contact pressure assumes a parabolic pressure distribution, which becomes weak at contact positions farther upstream and downstream from the nip portion center in the direction of rotation of the developing roller.
In the event of the developer amount regulation member having the aforementioned parabolic pressure distribution, upon so-called “push-in amount by developing roller” increasing, which is the virtual distance between the setting position of the blade before the developing roller being embedded and the setting position of the blade after the developing roller being embedded of the assembly of the developing apparatus, the local maximum value of contact pressure increases in proportion to the push-in amount by the developing roller.
Accordingly, it is expected that the variation in the push-in amount by the developing roller due to assembly also makes the maximum value of contact pressure vary. Consequently, it is necessary to obtain high assembly precision to set a desired local maximum value of contact pressure with little variation in a stable manner.
Also, in the event that the variation in setting positions of the developer amount regulation member and the developing roller arises in the longitudinal direction of the developing roller due to the variation in production, the circumferential deflection of the developing roller, and so forth, i.e., in the event that the variation in the push-in amount of the developing roller as to the developer amount regulation member arises in the longitudinal direction, the variation in the local maximum values of contact pressure of the developer amount regulation member and the developing roller arises over the longitudinal direction. Thus, the variation in toner degradation arises over the longitudinal direction, after endurance in particular. Consequently, concentration unevenness arises over the longitudinal direction in a solid image after endurance.
On the other hand, in recent years, one measure arranged to reduce the power consumption of an electro-photography apparatus is reduction of the power consumption in a fixing process. In order to realize low-power consumption in the fixing process, it is effective to reduce quantity of heat necessary for melting of toner, i.e., to lower the melting point of toner.
However, while toner having a low melting point facilitates low-temperature fixing, the strength as to toner stress is reduced. Accordingly, with a monocomponent developing system, toner is readily crushed and melted under the pressure affected from a developer amount regulation member. The variation in toner degradation conditions as to the variation in the local maximum values of contact pressure such as described above becomes still more pronounced.